I thought a well-aligned V-block and a drill press would be just the thing
to drill the holes straight. Two drill sizes is fine with me...
Nice summary!
73 de Dick, K6KR
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Grant Saviers
Sent: Saturday, February 19, 2011 11:48 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Force12 rivets
If you get on an airplane, you are trusting your life to rivets, some are
pop rivets.
Here is a manufacturer's website which covers much of the
engineering. http://www.cherryaerospace.com/
There are a number of issues with screw and hose clamp fastening systems:
1. As previously posted, screw threads tend to 'worry out holes'.
2. As widely noted, hose clamps are not so great - they loosen, in small
diameters can't be tightened much, increase wind resistance, and create a
dissimilar metal galvanic cell.
3. Not mentioned is the difficulty of drilling holes thru round tubes - a
big problem with screws and rivets
a. getting them centered and straight through two tubes (three if
sleeved for strength)
b. getting a round hole in thin material
c. getting a hole that is on diameter - obviously the larger the gap
between fastener and hole the worse the wear 4. Screws work on clamping
force generated friction between material layers as well as plain shear
strength, so how does that work when the tubes can be compressed?
5. SS screws also create a galvanic cell.
6. Sheet metal screws have so few threads engaged in a thin material so are
very poor for structural strength.
Aircraft rivet fastening processes use a pilot hole of a smaller than rivet
outside diameter followed by piloted core drill which acts much like a
reamer. This provides a hole that is really round and very close to a
diameter tolerance of less than a couple of 'thou. You can't do that with a
standard twist drill. The rivet then expands to fill the hole, (minimum
'worry") brings the layers being fastened in tight contact (increased
friction) , and provides clamping force that doesn't rely on compressing a
tube (constant over time). Either the rivet is solid and bucked from the
reverse side so its full diameter provides shear strength or a "pop" rivet
is used that provides the body shear strength of the Al plus the retained
pull core which can be of several different materials (steel, Al, SS,
Monel).
Why 3 rivets? Redundancy is good. Spreading the load is good. The tubing has
clearance so it telescopes and tightening it to ONE side is good.
The first rivet hole, if drilled and riveted then guarantees the inner
tube(s) won't move when drilling holes 2 & 3.
What is the downside of rivets? - care and the right drill are needed to get
holes on size and round. Home-Depot rivets are not a good choice.
A tool is needed to install them properly.
So are rivets a process "do not try this at home"? - NOT. While aircraft
piloted core drills are often available on ebay, DeWalt makes a drill which
works extremely well - pilot point drills. (formerly Black and Decker
Bullet Drills) They produce holes in thin materials that are round and very
close to drill diameter using a drill press, and if care is used in a hand
drill. Many suitable structural grade pop rivets can be set using a quality
hand tool.
My scratch build 40m Moxon is going together with rivets.
Grant KZ1W
On 2/19/2011 10:36 AM, Chet wrote:
> Yesssssssss!
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Gene Fuller
> Sent: Saturday, February 19, 2011 12:52 PM
> To: Dick Green WC1M; towertalk@contesting.com
> Subject: Re: [TowerTalk] Force12 rivets
>
>
> Assuming one rivet is strong enough to do the job the fact that they
> use three would indicate to me that not even the manufacturer doesn't
> trusts them. Perhaps a second for backup, but three.....? I would
> guess that cheaper is the answer. Lets get on with it - past time to cut
the thread.
>
> ----- Original Message -----
> From: "Dick Green WC1M"<wc1m73@gmail.com>
> To:<towertalk@contesting.com>
> Sent: Saturday, February 19, 2011 12:07 PM
> Subject: Re: [TowerTalk] Force12 rivets
>
> snip
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